1. Field of the Invention
The present invention relates to a method and an apparatus for cutting steel pipes in form of steel pipe piles, interlocked steel pipe piles or the like after constructed when used, for example, in underwater structures near seacoast, bridge construction works, reclamation works, reparian works and so on.
2. Description of the Prior Art
Steel pipe piles or interlocked steel pipe piles are used in formation of foundation supports and/or cofferdams or sheathing boards under the ground or in the water to carry out civil work, foundation work or the like.
In general, each interlocked steel pipe pile comprises a steel pipe trunk and junction joints attached to the outer periphery of the steel pipe trunk and extending in parallel to the axis of the steel pipe. The interlocked steel pipe piles are driven by a pile driver into the ground or the bottom of the water, engaging with neighboring ones at their junction joints. The interlocked steel pipe piles may have the same function of retaining of earth or water as ordinary sheet piles so as to positively produce a working space therein.
In comparison with ordinary sheet piles, such interlocked steel pipe piles are advantageously tough against buckling at driving, flexurally rigid, light-weight, and easy to cut at any desired position of the pile due to the hollow construction thereof after completion of the work, and can be reinforced by filling therein.
Conventionally, upper excess portions of the steel pipe piles or interlocked steel pipe piles are cut off from inside after completion of the work by a cutter, for example, a rolling disc pipe cutter or a grinder cutter, or the combination thereof.
For example, a cutting device which can cut both the steel pipe trunk and junction joints of an interlocked steel pipe pile by use of a grinder cutter having means for rotating the same both in a circular course and on its axis is disclosed in Japanese Patent Publication No. 50-31239. Another cutting device including a disc cutter and a grinder cutter is disclosed in, for example, Japanese Patent Publication No. 61-33933, in which the steel pipe is cut by the disc cutter and then junction joints cut by the grinder cutter. In these techniques in which the grinder cutter is used to cut the steel pipe or the junction joints, the cutting edge of the grinder cutter is thrusted in the steel pipe or the junction joint, so that, just before the cutting work is completed, the cutter is bitten in the cut steel pipe gap due to residual stress or dead weight of the steel pipe, and consequently the cutter may be broken, causing the problems of increase of cutting cost and reduction of operativity.
A further cutting device which employs high pressure fluid injected from a water jet nozzle to cut the steel pipe trunk and the junction joints is disclosed in, for example, Japanese Patent Laid-Open Publication No. 61-87020. A still further cutting device in which the steel pipe wall is cut by a disc cutter and then the junction joints are cut by high pressure fluid is disclosed in, for example, Japanese Patent Laid-Open Publication No. 61-86122. These techniques employing water jet are useful to cut the steel pipe to which the nozzle can be brought close to inject water jet against the steel pipe, but in cutting of the junction joint, the nozzle cannot be brought close enough to the junction joint, causing reduction of the cutting capacity of water jet which results in difficulty in complete cutting and drastic increase of time required for cutting and consequently increase of cutting cost.